I have TowBoatUS and have been towed 3 times, the first out of my own pocket . This prompted me to join. Service all the times was great. I look at my yearly fee as a part of insurance coverage for the boat. When I signed up, I don't remember Seatow being on the lake.
I believe that Andrew's Marine Service out of Minge Cove also offered towing service, but I don't know if he still does.
To answer your question, you really need to look at the two major players, Seatow & TowBoatUS, look at their respective coverages & benefits, their costs, and what best fits your needs.
I have compared the two a few years back and did not find a compelling reason to switch.
Good luck.

Seatow covers tows from your home dock, TowBoatUS covers 50%. Depending on where your repair center is to your home dock could cost you of bucks. Yes SeaTow is more expensive($119) but its one charge that covers everything, no haggling etc.

Both Seatow and TowBoat offer competitively priced plans that will not charge you extra for towing. From FL I know Seatow will go to the Bahamas (depending how far you are from FL) and tow you back at no extra charge.

For me it is a must because even a short tow is very expensive. Towed once on the lake and 3 times from the ocean.

I have TowBoatUS. They took my boat from my island camp to my marina, and paid full, because the camp was not considered my "Home port". TowBoatUS dispatcher could not understand what an island was and that there was no car access. Amusing and frustrating at the same time trying to explain. My son had a breakdown in Weirs Bay and called TowBoatUS. They were busy and handed it off to Irwin at MVYC (home marina). They paid the Irwin bill as I recall. Also used Seatow which was called by MP since TowBoatUS wasn't available, too early in the season. My boat insurance (Progressive) covered it.
I think I pay an extra $17 a year to BoatUS for "complete" towing, no deductible or 50%. It could be more now; my membership is on auto-renewal.

In short, TowBoatUS is cheaper. Having experience with both, cost aside, I'd call SeaTow, better boat, equipment, divers, airbags to lift you off the bottom and seems to have a longer operating season. Being a seasonal job, this could change from year to year.

I met a 'tow guy' on Champlain last year, though I wasnt being towed, and he was a 'contractor' on a list for one of those companies, I dont remember which. It sounded to me like a AAA automotive kind of deal where AAA calls a tow truck contractor that is available & close to you. This means the actual service could be highly variable. Does anyone know if either of these companies work this same way on Winni?

The policy includes towing and you can use whoever you would like when you have a problem. You just submit the receipt after using them. I am not sure the towing companies will let you use other towing companies if they are busy.

At the time I started with NBOA they were the best and least expensive option for boat insurance. That was many years ago so I don't know if that is still true. It would probably be worth looking at what you are paying for insurance and towing combined and see if you can save money with an all in one policy.

I added my boat to my existing homeowners policy. The premium was $375 for agreed coverage of 55K. They also have towing coverage up to $250 per incident. It is an option. I have an inquiry in as to the premium.

FYI added towing to my insurance policy for $15/year up to 250 per incident

A tow from Robert's Cove to Downing's Landing a few years back was shown as $385. Seeing as how I had towing coverage, it was nothing out of my pocket.
What led me to buy coverage was a tow from next to the shoal area just east of Rum point to Alton town docks was also around the same amount and all out of our pocket.